This invention pertains to flywheel energy storage systems and more particularly to a safety mechanism for flywheel systems that use a tilt switch to protect the system from damage by halting operation if not oriented sufficiently close to vertical. Depending on the type of bearings employed in the flywheel energy storage system, the invention can prevent system damage from overloading of the bearings, non-centered operation or greatly shortened bearing life from excessive bearing loads.
Flywheels have emerged as a very attractive energy storage technology for such electrical applications as uninterruptible power supplies, utility load leveling systems, and alternative energy generation. Flywheel systems convert back and forth between the rotational energy of a spinning flywheel and electrical energy. A flywheel energy storage system includes a flywheel, a motor and generator, a bearing system and a vacuum enclosure. The rotating flywheel stores the energy mechanically; the motor and generator converts between electrical and mechanical while the bearing system physically supports the rotating flywheel. High-speed flywheels are normally contained in a vacuum or low-pressure enclosure to minimize aerodynamic losses that would occur from atmospheric operation.
Some of the benefits of flywheel energy storage systems over conventional batteries are longer life and higher reliability. A key component to achieving long life with flywheel energy storage systems is the bearing system. Flywheels have been supported by numerous configurations of bearings that have included magnetic, mechanical and fluid type. No matter which bearing system method is used, the orientation of the flywheel system with respect to gravity alters its performance. In most designs, it is preferable to orient the axis of rotation of the flywheel as close to vertical as possible to insure proper operation. In this configuration, the weight of the flywheel is supported axially. As the orientation of the axis of rotation is tilted with respect to vertical, the radial component of the load exerted on the bearings increases, increasing the risk that the radial load capability of the bearings be exceeded, causing them to not carry the load in the case of magnetic bearings, or shorten the bearing""s life in the case of mechanical bearings. Besides increasing bearing loads or shortening system life, an excessively tilted system can cause unexpected operating conditions. Systems using long shafts can experience unanticipated increased radial deflections. Such deflection can cause component clearances to be less than designed and also lead to failures due to metal fatigue and other factors.
In many cases, flywheel energy storage systems are installed below ground for safety. Whether below ground or above ground, the chance for improper installation or a change in the system orientation to occur over time exists. Continued operation of a flywheel system that is oriented too far from vertical can greatly shorten the life of the system and potentially can cause dangerous failures to occur.
Accordingly, the invention provides detection and a warning signal in the event of operation outside a predetermined tolerance from vertical orientation of a flywheel energy storage system having a flywheel supported for rotation about a vertical axis using a bearing system, and an attached motor/generator that accelerates and decelerates the flywheel for storing and retrieving energy. To prevent excessive radial loading of the flywheel bearings, a tilt sensor is included in the flywheel system that detects if the orientation of the axis of rotation is beyond off-vertical tolerance. The tilt sensor acts as a safety mechanism and can generate a signal for corrective action, including activating alarms or slowing or stopping operation of an improper tilted-axis orientation of the system. Operating flywheel systems with a tilt angle that exceeds the design of the bearing system can drastically reduce the bearing life and can potentially lead to failures. Despite the best intentions of engineers and those responsible for installation, incorrect installation of flywheel systems may occur from time to time. Earthquakes, ground shifts and technician installation errors are all potential causes for an unacceptably tilted flywheel system. These occurrences may go undetected and unrepaired. In several embodiments of the invention, the tilt sensor generates signals that trigger remote or unit alarms, disconnect power to the motor, or discharge the flywheel energy storage system.